Category I – Simple benign cyst with the following features: |
Hairline thin wall. |
Density less than 20 Hounsfield units (similar to water). |
Does not contain septa, calcification, or solid components. |
Does not enhance. |
Category II – Cystic lesions with the following features: |
A few hairline thin septa. |
"Perceived" enhancement may be present. There is no measurable enhancement. |
Uniformly high attenuation lesions <3 cm that are well marginated and do not enhance fall into this category. |
Category IIF – Minimally complicated cysts that do not neatly fall into category II. These lesions are generally well marginated but have some suspicious features that require follow-up: |
Multiple hairline thin septa or minimal smooth thickening of the wall or septa. |
"Perceived" enhancement of septa or wall may be present. |
Thick and nodular calcification of the wall or septa, but no measurable contrast enhancement is present. |
Totally intrarenal, nonenhancing, high attenuation lesions >3 cm in diameter fall into this category. |
Category III – Cystic masses that typically undergo surgical evaluation, although many lesions are benign. These lesions show the following: |
Thickened irregular or smooth walls or septa in which measurable enhancement is present. |
Category IV – These mostly malignant lesions have the following features: |
All category III criteria. |
Enhancing soft-tissue components adjacent to, but independent of, the wall or septum. |
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